The present invention relates to a ball screw power drive which is preferably employed for raising and lowering ventilation curtains or other air flow control devices in poultry houses, or the like.
Poultry houses, other animal houses and greenhouses often employ ventilation systems which include very large curtains that are selectively raised and lowered to control air flow through the house. These curtains are usually thermostatically controlled so that their position is automatically adjusted in an effort to maintain the temperature in the house within a desired range. It is very important that the temperature in the house be maintained within a desired range, especially in the case of poultry houses because poultry is very sensitive to temperature extremes, particularly elevated temperatures which occur in the summer months.
Power failures in a poultry house pose a significant problem in this regard. In particular, if a power failure occurs during a very hot day, the ventilation system will shut off and the chickens will be quickly exposed to elevated temperatures which can result in death, often within a very short period of time, for example, fifteen minutes. This problem is compounded by the fact that prior art curtain power drives work in such a manner that the curtains will be fixed in their previously set position upon the occurrence of a power failure, unless various configurations of expensive supplemental equipment are installed. If the curtains happen to be in a position which substantially impedes air flow through the poultry house when a power failure occurs, the temperature in the house will increase to a dangerous level substantially faster than would occur if the curtains are fully, or nearly fully, open.
To remedy this problem, prior art curtain drives provide a means by which the curtains can be manually opened upon the occurrence of a power failure. This solution is not completely satisfactory, however, because not only does it require a quick detection and response on the part of the poultry house employees, but also requires that the curtains be manually reengaged with the automatic drive mechanism when power is restored.
Another drawback with prior art curtain power drives is that they typically employ a drive mechanism which cannot adequately handle heavy loads. The ventilation curtains employed in poultry houses are usually very large, ranging anywhere between four hundred and nine hundred feet long, and typically require a five thousand pound lifting force to be moved from an open to a closed position. Although numerous types of drive mechanisms, such as spin drives and acme screw drives, have been employed in the past in ventilation curtain power drives, none of these have been completely satisfactory from a load strength standpoint.